The invention relates to electro-hydraulic actuators for turbine valves.
In conventional turbine construction, the hydraulic energy is supplied to the actuators of the individual turbine valves by means of a central hydraulic supply system. This system includes a central hydraulic fluid container and usually several fluid pumps working against hydraulic pressure accumulators. It follow that a least two pipework lines are necessary for the connection of each actuator to the central hydraulic supply system, one pipework line undertaking the supply of hydraulic fluid under pressure to the actuator while the other pipework line returns the drained hydraulic fluid into the central hydraulic fluid container when the hydraulic component is unloaded. In order to utilize actuators which are less sensitive to dirt, it is advantageous to operate with relatively low operating pressures. Low pressure operation does, however, require that large oil tanks be provided.
It if is desired to serve all the actuators of a turbine from one central hydraulic supply system, the installation necessarily has many long oil pipes. In order to guarantee the transmission reliability of the hydraulic energy, these pipes demand substantial expenditure on design, construction, quality control and maintenance. Apart from pressure oscillations and pressure peaks in long pipes, it is, in particular, also necessary to make allowance for the loading due to thermal expansion. Finally, it is also necessary for safety reasons to make allowance for the fire danger arising from a pipe failure in the hot area. The fire danger can of course be reduced by the use of double-walled pipes, but this fire protection technique introduces substantial problems with respect to pipe laying and accessibility. With respect to fire protection, the use of low-flammability hydraulic fluids can be considered. Such hydraulic fluids, however, are expensive and require a regenerating plant because of their poor ageing resistance. The instructions of the suppliers must be observed most precisely and they are especially subject to decomposition due to heat effects.
The solutions revealed in European Pat. Nos. 0,040,732 AI and 0,040,737 AI avoid the disadvantages described above in that the need for the previously necessary hydraulic supply lines, and the expense associated with these supply lines, can be obviated by the integration of the hydraulic supply system into the actuator. This arrangement, however, has disadvantages:
(a) Each actuator must have its own hydraulic supply system allocated to it. With the turbine's multiplicity of rapid action stop valves and control valves, it follows that an equally large number of hydraulic supply systems have to be provided. Accordingly, financial expenditure is correspondingly large. PA1 (b) Since each hydraulic supply system forms an autonomous unit, a second fluid pump must be provided for switching on in the case of fluid pump failure and this second pump must be driven by a second electric motor. Although this measure does increase the operational reliability of the actuator, a corresponding increase in the installation volume and the cost of the hydraulic supply system must be accepted in exchange. PA1 (c) For the same reasons as discussed under (b), the hydraulic pressure accumulator must be sub-divided into at least two partial accumulators, the storage volumes of the partial accumulators being so dimensioned that even in the case of one partial accumulator failing, a sufficient quantity of hydraulic fluid is available for the operation of the hydraulic actuator cylinder. The consequence resulting from this is again an increase in the installation volume and the cost of the hydraulic supply system. PA1 (d) From the above considerations, it is therefore questionable whether the desired minimization of the installation volume of the hydraulic supply system--insofar as this can be integrated with the actuator into a compact actuator block located on the valve housing--is at all possible against the background presented. PA1 (e) In addition, the vibrations emitted by the valves during operation are propagated, especially in the case of load changes following one another in quick succession, to the relatively sensitive elements of the hydraulic supply. The life of these elements decrease and interruptions to the operation result.
The objectives of the present invention is to remove the disadvantages mentioned above and to produce an electrohydraulic actuator for turbine valves which, on the one hand, satisfies the high requirements with respect to control force and control speed and, on the other, avoids the problems associated with the transmission of hydraulic energy.
The turbine valve electro-hydraulic actuator, proposed in accordance with the invention for attaining this objective, is characterized in that at least one control valve and at least one rapid action stop valve, whose actuators are of the same design and are integrated into a compact actuator unit located on the valve housing, are allocated per tubine inlet valve, the actuators being connected in pairs to a hydraulic supply located directly adjacent to them and controlled by a volumetrically controlled oil supply unit integrated with the hydraulic supply.
The advantages of the invention are to be seen essentially in that, as a result of the proposed solution, the attachment of one control valve and one rapid action stop valve to each turbine inlet valve can be brought about without problems in terms of the space that is required and is available.
Due to the fact that the two actuators are of the same design, the highest possible degree of interchangeability is attained.
A further advantage of the invention is that each hydraulic supply serves one control valve and one rapid action stop valve. Due to the fact that the hydraulic supply is no longer restricted in terms of space, it can be made more sturdy, simpler and cheaper.
A further advantage of the invention is that the hydraulic supply contains a volumetrically controlled oil supply unit which supplies the quantity of fluid necessary for action on the control valve. This oil supply unit also includes an auxiliary pump, which supplies the hydraulic quantity for action on the rapid action stop valve, for the electro-hydraulic valve and for the adjustment cylinder of the pump adjustment unit. The energy consumption of the unit is minimal because the adjustment pump supplies only that quantity and that pressure which is required by the control valve.